This invention relates to a process for the production of compounds containing at least one urea group and at least one silyl group, in which a compound containing at least one amino group is reacted with a carbamate, either the compound with at least one amino group or the carbamate bearing a silyl group, to compounds produced by this process, to their use and to surface coating compositions, foams and adhesives containing these compounds.
Organic compounds, especially polymers, which contain both a silyl group and a urea group are used in many branches of industry, for example in the coating or adhesives field. The advantages of such compounds, especially the polymers, lie in particular in their ability both to hydrophobicize and to impart a binding effect to hydrophilic substrates and also to crosslink with one another under the effect of moisture.
Surface coating compositions containing the above-mentioned compounds show improved adhesion both on hydrophobic and on hydrophilic surfaces. Adhesives containing such polymers are capable, for example, of permanently bonding both hydrophilic and hydrophobic substrates and substrates of different polarity to one another.
Hitherto, the simultaneous introduction of urea groups and silyl groups into polymers has been difficult for a variety of reasons. In many cases, isocyanatosilanes have been used to introduce such groups even though they were unpopular among manufacturers of such products because of their toxicity and their sensitivity to water. In addition, residues of isocyanatosilanes often could not be removed to a satisfactory level from the compounds thus produced so that a residual content of isocyanates often resulted in an obligation to declare the compounds themselves or products produced from them. However, the declaration of such ingredients reduces consumer acceptance of the products produced from them.
However, the problem illustrated here with reference by way of example to the interplay between urea groups and silyl groups also applies in principle to many other methods of introducing structural elements obtainable using isocyanate groups into polymers. The presence of isocyanates in reaction mixtures often leads to the formation of unwanted products or to isocyanate-containing material remaining in the end product so that the problems mentioned above arise.
A process for the production of polyethers containing both a urea group and an alkoxysilyl group is described, for example, in Chemical Abstracts 123:171406 (abstract of JP 93-185 595). To produce these compounds, an aminofunctional polyether is reacted with a silyl compound containing as isocyanate group.
U.S. Pat. No. 5,886,205 relates to a process for the production of isocyanate compounds containing silyl groups which comprises the thermal decomposition of carbamic acid esters containing silyl groups in the presence of a catalyst. The reaction of a carbamate with a compound containing at least one amino group is not mentioned in this document.
U.S. Pat. No. 5,218,133 relates to a process for the production of silyl carbamates or silyl isocyanurates, in which an aminosilane is reacted with a dialkyl carbonate, diaryl carbonates or a mixture thereof in the presence of a basic catalyst to give a silyl organocarbamate. The basic catalyst is then optionally neutralized and residual aminosilane is neutralized. After addition of a decomposition catalyst and heating under reduced pressure, a silyl isocyanurate is obtained. However, the cited document does not describe how silyl compounds containing urea structural elements can be obtained by reaction of carbamates with amino compounds, either the amino compound or the carbamate or both containing a silyl group.
U.S. Pat. No. 6,008,396 describes a process for the production of an isocyanato-organsosilane, in which a carbamato-organosilane is converted into an isocyanato-organosilane in an inert liquid medium. The production of compounds containing both a urea group and a silyl group is not mentioned in the cited document.
U.S. Pat. No. 5,886,205 describes a process for the production of an isocyanate containing silyl groups in which a carbamic acid ester containing silyl groups is decomposed in the presence of a catalyst at a pH value of at most 8. A process for the production of compounds containing both urea groups and silyl groups is not described in the cited document.
In addition, many combinations of structural elements obtainable using isocyanate groups and silyl groups have hitherto only been obtainable by multistage and hence expensive processes. This applies in particular to the production of polymers containing both isocyanurate groups and urea and silyl groups. Such polymers are of considerable interest with regard in particular to their crosslinking and hence to the resulting material properties of surface coating compositions and adhesives.
EP-A 1 006 132 relates to alkoxysilane-containing lacquer preparations produced using 4,4′-diisocyanatodicyclohexyl methane polyisocyanates. The cited document describes, for example, the reaction of polyisocyanates obtainable by trimerization of 4,4′-diisocyanatodicyclohexyl methane with aminofunctional alkoxysilanes. Unfortunately, the described reaction has the disadvantage that isocyanurates generally containing low molecular weight diisocyanates are used. Low molecular weight isocyanates such as these have a considerable toxic potential. In addition, the crosslinking of a polymer produced using such isocyanurates is difficult to control because the isocyanurates described in the cited document always represent a complex mixture of compounds differing in their functionality in which isocyanurates having a functionality of more than three are always present. The use of such mixtures involves the disadvantage for the user that the properties of a polymer produced using these triisocyanatotriisocyanurate mixtures are difficult to adjust in view of slight crosslinking. Another disadvantage of the compounds described in the cited document is that a urea group or a urethane group is always present in the immediate vicinity of the isocyanurate group because of the structure of the isocyanurates used. This constellation complicates or prevents the production of highly flexible binders because this direct proximity of the functional groups mentioned generally leads to hard brittle binders.
In addition, the presence of urethane groups reduces the thermal stability of these compounds because urethane groups split at ca. 140–160° C. Unfortunately, such behavior prevents the use of such compounds in heat-resistant applications.
Another disadvantage of the described compounds is that isocyanurates containing isocyanate groups are difficult to produce. On account of the danger of crosslinking, which increases with increasing conversion, the trimerization of isocyanates to isocyanurates can only be carried out to a certain degree below a corresponding crosslinking point. The isocyanate originally used for crosslinking and the isocyanurate containing isocyanate groups obtained as product then have to be separated in complicated distillation processes. After distillation, the isocyanate distilled off is returned to the trimerization process. The volume/time yields of such a process are poor on account of the complex separation steps.